Generally, an analog signal is used for transferring information and data across a communication channel. The analog signal can be converted into a digital signal at a receiving device such as a mobile phone, laptop, or television. Conversion from an analog to a digital signal is accomplished by sampling the analog signal at predetermined time intervals. Once a digital or discrete signal has been generated, the sampling rate can be increased by interpolation. During interpolation, a set of new data points are constructed within a set of known data points by adding a number of samples between two or more known samples of a discrete-time signal. Generally, interpolation is performed when the digital signal is to be oversampled, for example while reconstructing an analog signal from the digital signal using a digital to analog converter (DAC).
Typically, sinc or cascaded integrator comb (CIC) interpolators are used for oversampling. Sinc interpolators have an ability to handle arbitrary or large sampling rate changes and do not require complex hardware for implementation, thereby facilitating generation of a reliable undistorted analog signal in a DAC. Sinc interpolators include a cascade of differentiators followed by an up-sampler, which is in turn followed by a cascade of integrators.
During operation of a sinc interpolator, an offset can creep into the output generated by the cascade of integrators due to word retention in the integrators. The error due to word retention can get accumulated over a period of time resulting in large errors. Additionally, the output can suffer from quantization errors on account of discrete values being assigned to displaced samples in the digital signal.
Typically, to minimize word retention and quantization errors, the integrators are reset once an offset is detected. Resetting the integrators during operation of the sinc filter can lead to loss of data. Further, most current methods for offset detection and reset apply to first and second order interpolators, which are linear interpolators. Third and higher order interpolators provide for non-linear interpolation of input samples of the analog signal, and an attempt to reset such higher order integrators tends to distort the generated output.